After two hours, the cells were harvested, lysed, and biotinylated proteins were isolated as described in [19]. to cell cycle arrest and apoptosis. Based on site-directed mutagenesis and modeling studies, we propose a mechanism of SK053-mediated PRDX crosslinking, including double thioalkylation of active site cysteine residues. Altogether, our results suggest that peroxiredoxins are novel therapeutic targets in Burkitt lymphoma and provide the basis for new approaches to CZ415 the treatment of this disease. < 0.05. The cell cycle distributions in Raji cells expressing PRDX1-specific shRNA2 (shPRDX1) and control cells expressing non-targeting shRNA (control shRNA) were evaluated with a propidium iodide circulation cytometry-based assay. The error CZ415 bars show the SD (= 2), *< 0.05. E. Namalwa cells were subjected to sequential lentiviral transductions to downregulate PRDX1 and PRDX2, CZ415 as explained in C. and the number of viable cells was assessed in a hemocytometer for three consecutive days. The degree Rabbit Polyclonal to PTRF of PRDX1 and PRDX2 knockdown was assessed by immunoblotting in cells collected 3 days after puromycin selection. PRDX1 is usually a target for SK053 Considering the elevated levels of TRX-like enzymes as well as their pro-survival role in lymphoma cells, we searched for candidate compounds for their pharmacologic inhibition. We have previously reported on the synthesis of the thiol-specific small molecule peptidomimetic with antitumor activity, SK053. Here, we have found that BL cell lines are sensitive to SK053, with an LC50 ranging from 7 M for the Namalwa up to almost 20 M for Bjab cells. Importantly, normal germinal center B cells (GC B cells) isolated from human tonsils were more resistant to SK053 (LC50 > 60 M), indicating selectivity towards malignant B cells (Physique ?(Figure3A3A). Open in a separate windows Physique 3 SK053 covalently binds to PRDX1 in Raji cellsA. Cytostatic/cytotoxic effects of SK053 on human BL cell lines and normal germinal center B cells (GC B cells). BL cell lines were incubated with SK053 for 48 h and subjected to a MTT viability assay. The LC50 was calculated in Graphpad Prism 5 by nonlinear regression dose-response analysis with variable slopes. The SEM was calculated based on two impartial experiments. GC B cells isolated from human tonsils (= 3) were isolated and cultured as explained in Methods. Quantity of viable cells after 48 CZ415 h treatment with SK053 was assessed using Muse? Cell Analyzer (Merck Millipore). LC50 was calculated in Graphpad Prism 5, as explained above for BL cell lines. B. Chemical structure of SK053, its biotinylated derivative SK-bio, and the inactive biotinylated analog devoid of the electrophilic center, SK-in. C. Raji-sub cells were incubated with SK-bio or SK-in for 2 h, lysed, and biotin-labeled proteins were affinity-purified on avidin-coated beads. Total protein was resolved by SDS-PAGE and visualized by silver staining. The arrow indicates the band that was excised and recognized by mass spectrometry. D. Tandem mass spectra of the Cys-173-made up of peptide, HGEVCPAGWKPDGSDTIKPDVQK. The site of cysteine modification is marked with a star. The upper panel spectrum corresponds to a peptide altered with iodoacetamide (+57.021), with the parent ion m/z 802.731 and a charge 3+. The bottom panel presents the spectrum of a peptide in which cysteine bears an inhibitor (+466.225), with parent ion m/z 704.600 and a charge 4+. E. The same samples as in C. were subjected to immunobloting using antibodies specific to PRDX1 and -actin (ACTIN). To identify targets for SK053 in BL cells, we synthesized biotin-tagged derivative of SK053 (SK-bio) and an inactive, biotinylated analogue that lacks the electrophilic double bond (SK-in), which was used as a negative control (Physique ?(Physique3B,3B, Supplementary Physique S3). Only the active, SK-bio preserved cytostatic/cytotoxic activity (Supplementary Physique S4). A band of approximately 20 kDa was detected in a silver-stained gel only for cells incubated with active SK-bio (Physique ?(Physique3C).3C). The protein was recognized by MS as PRDX1, with > 90% of sequence coverage. Furthermore, in a collection of tryptic peptides, we searched for a modification of 540 Da, corresponding to the mass of SK053, after the first addition reaction, and the modification of 466 Da, which corresponds to the a part of SK053 after the addition and removal of the leaving group, according to the previously explained mechanism (Plan 3 in [20]). We found the tryptic peptide, made up of Cys173, with a mass modification of 466 Da. The fragmentation of the peptide confirmed that the modification is usually on Cys173 (Physique ?(Figure3D).3D)..